At present, as a new type of light source, the LED is widely used in various fields due to having the advantages of high brightness, low energy consumption and long life. As LED has a constant forward conduction voltage, only when a total forward conduction voltage of a LED strip is reached, the LED strip can light. To ensure that the LED strip can work steadily, a constant current control on the LED strip is needed, and the traditional linear constant current controlling method for the LED strip is achieved by connecting a linear constant current controlling circuit between the output terminal of the rectifier bridge and the input terminal of the LED strip (as shown in FIG. 1), or between the output terminal of the LED strip and the ground (as shown in FIG. 2). And in the case of using the mains power supply, when the linear constant current source is used to control the LED strip, only when the main input voltage rectified by the rectifier bridge voltage is greater than the conduction voltage of the LED strip, a current will flow through the LED strip; when the voltage rectified by the rectifier bridge voltage is less than the conduction voltage of the LED strip, no current will flow through the LED strip, which lowers the utilization and power factor of the LED.
In order to solve the problem existing in the traditional linear constant current controlling method for the LED strip, two solutions are provided in the prior art. The first method comprises connecting a high voltage electrolytic capacitor to the output terminal of the rectifier bridge, and filtering an input sine wave voltage into a DC voltage larger than the conduction voltage of the LED strip through the electrolytic capacitor, such that the LED in the LED strip can be continuously on and a current flows through the LED in the whole clock cycles. This can improve the utilization rate of the LED, but reduces the power factor and at the same time increase the cost of the system. In addition, due to the short service life of the electrolytic capacitor, the service life of the power supply is reduced. The second way comprises decreasing the amount of the LEDs in the LED strip to reduce the total forward conduction voltage of the LED strip, such that the time when the LED in the LED strip can be continuously on and current flows through the LED in each clock cycle increases. However, the solution decreases the utilization rate of the input voltage, and makes the driving circuit of LED strip suffer from a large voltage, increases the power consumption of the driving circuit, and reduces the efficiency of the system.
In conclusion, the existing technology has the problem of low power factor and low efficiency system.